1. Field of the Invention
The present invention relates generally to reinforcing walls to increase their ability to withstand atypical loads such as those encountered during earthquakes. More particularly, the present invention relates to a method for increasing the ductility and strength of a wall in situ without removing the wall from service and without the need to provide auxiliary support during the repair process.
2. Description of the Related Art
Recent earthquakes have revealed that many existing walls lack sufficient strength and ductility to withstand moderate to severe earthquakes. Moderate quakes have caused all types of load-bearing and non-load bearing walls to crack while stronger quakes at times have resulted in the total failure of such walls.
Because the collapse of walls can have disastrous consequences, it has become a common practice in the construction of certain walls, e.g., cellular brick or concrete walls, to reinforce the walls with metal rods or bars. However, there are hundreds of thousands of existing in earthquake-prone areas which do not have adequate metal reinforcement and which were not designed to withstand high degrees of atypical loading. Furthermore, while metal reinforcement provides added structural strength to walls, metal-reinforced walls also have been known to crack or fail when subjected to atypical loadings generated during earthquakes.
In most cases, the replacement of existing walls with walls having greater strength and ductility is economically impracticable. Accordingly, there is a need to provide a simple, efficient and relatively inexpensive method for reinforcing walls so as to prevent or reduce the likelihood of failure during an earthquake. One example of a method for increasing the structural strength of existing structures without their removal from service is set forth in U.S. Pat. No. 5,043,033, issued to Fyfe. In this particular patent, the surface of a concrete column is wrapped with a composite material to form a hard annular shell surrounding the concrete column. The space between the outer composite shell and the concrete column is then pressurized by injecting a hardenable liquid.
Another approach to reinforcing the exterior of an existing concrete support column without removing it from service is set forth in U.S. Pat. No. 5,218,810, issued to Isley, Jr. In this patent, the exterior surface of a concrete column is wrapped with a composite material to form a hard annular shell or sleeve which is in direct contact with the column surface.
While these approaches may be well suited to the reinforcement of existing structures which can be completely surrounded by a composite shell, i.e., columns, they do not account for the problems associated with reinforcing certain structures, i.e., walls, wherein it is structurally or economically infeasible or impracticable to form a unitary composite shell about the exterior of the structure.
For instance, a unitary composite shell cannot be formed around the portions of exterior or interior walls which include windows, doors, or other structural discontinuities provided for the ingress or egress of light, air, or people. Accordingly, there remains a need for a fast, efficient, and cost-effective way to reinforce walls so as to increase their resistance to structural failure during earthquakes.